Network having redundancy properties, Ethernet switch for such a network and method for configuring such a network

ABSTRACT

There is described a network having redundancy properties, an Ethernet switch, and a method for configuring the network. At least two network segments which are formed with a plurality of Ethernet switches are connected to one another by means of a redundant connection comprising at least two coupling channels. During configuration, a programming device stores a logic name for the redundant connection in the respective memory of associated coupling devices. In a network startup phase, said coupling devices determine the respective other connection partner associated with the same redundant connection by distributing special messages in which they enter the logic name of the redundant connection. They use an order criterion to determine which coupling channel is active and which coupling channel is deactivated during trouble-free operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2006/068940, filed Nov. 27, 2006 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10 2005 057 122.0 DE filed Nov. 30, 2005, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a network having redundancy properties, whereinsaid network conforms to an Ethernet specification and contains at leasttwo network segments which are formed using a plurality of Ethernetswitches and are connected to each other via a redundant connectioncomprising at least two coupling channels, to an Ethernet switch forsuch a network and to a method for configuring such a network.

BACKGROUND OF INVENTION

Various networks having redundancy properties are already disclosed inEP 1 260 081 B1. Inter alia a so-called Optical Switch Module (OSM)having a plurality of ports for the attachment of further networkcomponents is described there. In order to construct an Ethernet or FastEthernet network, e.g. terminals are attached to the ports and aretherefore connected to each other via the OSM. A plurality of OSMs canbe interconnected in a continuous line structure to form a string. Anoptical ring is produced if the two line ends are attached to an OpticalRedundancy Manager (ORM). Test messages which the ORM inputs into thetwo line ends are used to check whether there is an interruption in thestring. If there is no error, i.e. if the string is not interrupted, theORM separates the two line ends and if there is an error, the two lineends are connected together by the ORM. In a network comprising aplurality of redundant optical rings, two optical rings are coupledtogether via two OSMs. The two OSMs which are connected between theoptical rings form a communication channel in each case, of which one isactive and one is switched to a standby mode. The two OSMs exchangetheir status via special standby ports which are connected to each otherby means of cables. If the connection via the active OSM fails, theredundant OSM enables its communication channel, i.e. it switches fromstandby mode to active mode. A comparatively short reconfiguration timeis achieved in this way. This prevents physical errors, temporaryelectromagnetic interference, network upgrades or component replacementsfrom impairing the communication between the network components for anunacceptably long time. The disadvantage in this case is that twoadditional devices are required for the redundant connection of twooptical rings, and that these devices must additionally be connectedtogether. In order to avoid this disadvantage, the above cited patentdocument proposes that a switch module which is located at the activecommunication channel cyclically sends so-called port-select messages tothe other switch modules that are arranged in the same string, while thecommunication channel is uninterrupted. The switch module which islocated in standby mode at the other communication channel monitors thefirst communication channel by analyzing the port-select messages.Although a comparatively short reconfiguration time is likewise achievedin the known network, the configuration of the switch modules in thestartup phase of the network is disadvantageously carried out using aresource-intensive algorithm and requires more time due to themultiplicity of messages that must be sent.

Further networks having redundancy management are disclosed in thepublications EP-A-0 403 763 and EP-A-0 560 122.

The standardized Spanning Tree and Rapid Spanning Tree protocolslikewise allow redundancy management in an Ethernet network. However,these methods cannot always be used in industrial communications due tothe long reconfiguration times, particularly if time intervals ofseveral seconds during which the data communication is disrupted are notacceptable.

SUMMARY OF INVENTION

An object of the invention is to provide a network having redundancyproperties and an Ethernet switch for such a network, which can beconfigured easily and in a manner which requires few resources during anetwork startup phase.

This object is achieved by the new network having redundancy properties,the new Ethernet switch and the new method for configuring such anetwork, these having the features cited in the independent claimsrespectively.

The invention has the advantage that it allows a particularly simpleconfiguration of redundant connections between segments of an Ethernetnetwork in which Ethernet switches are arranged. In a particularly clearmanner, the configuration merely requires a user to enter or specify alogical name of the redundant connection. This can be freely chosen andis designated as a connection name. Two Ethernet switches are configuredas a device pair in a network segment. This device pair monitors itselfduring redundancy operation in accordance with the configuration in areciprocal manner using Ethernet messages and, in the event of an error,reroutes the data traffic from one Ethernet connection to the other(redundant) connection in each case. If a coupling port in the Ethernetswitch is also configured for each redundant connection, port-selectiveswitching between the Ethernet switches that are involved in a redundantconnection is advantageously possible.

An Ethernet switch in whose memory a logical name for a second orfurther redundant connection can be stored has the advantage that thefurther redundant connections can be configured in the same way as thefirst redundant connection was configured and that each redundantconnection has its own redundancy for link-down events. If a link-downoccurs at a coupling port, i.e. if the redundancy is lost for a couplingchannel, this actually has no effect on the redundancy of the otherredundant connections, since the redundancy can be switched in aport-selective manner.

By virtue of a specially defined multicast address which is used as adestination address in the special messages, the transmission range ofthe special messages in the Ethernet network can advantageously berestricted, e.g. to switches which are capable of setting up a redundantconnection. In this case, a particularly simple defining criterion fordetermining which coupling channel is active in error-free operation andwhich has been deactivated is established if the MAC source addresswhich is received in the special messages is analyzed and compared withthe local MAC address in the Ethernet switches that are involved in aredundant connection. For example, the Ethernet switch which has thehighest MAC address can be defined by default setting as the master,which then provides the active coupling channel in error-free operation.Alternatively, the defining criterion can be configurable for thispurpose, e.g. by assigning numeric values to the switches.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and configurations and advantages thereof are explained ingreater detail below with reference to the drawings, in which anexemplary embodiment of the invention is illustrated and in which:

FIG. 1 shows a network having redundancy properties,

FIG. 2 shows a flow diagram of the redundancy configuration, and

FIG. 3 shows a network comprising three network segments.

DETAILED DESCRIPTION OF INVENTION

In accordance with FIG. 1, an exemplary network having redundancyproperties consists of two network segments NS1 and NS2, each of whichcontains six Ethernet switches ES1 . . . ES6 and ES7 . . . ES12respectively. The switches feature in each case a memory M for storingconfiguration data and ports P1 . . . P4 for coupling to other Ethernetswitches or terminal subscribers. It is obvious that switches having adifferent number of ports can be installed as an alternative. For thepurpose of data transmission between two Ethernet switches, a port ofone of the switches is connected to a port of the other switch in eachcase. For example, the port P3 of the Ethernet switch ES2 is attached tothe port P3 of the Ethernet switch ES4. Two coupling channels K1 and K2form a redundant connection between the two network segments NS1 andNS2. The first coupling channel K1 is formed by a connection of the portP4 of the Ethernet switch ES5, which is arranged in the network segmentNS1, to the port P2 of the Ethernet switch ES7, which is arranged in thenetwork segment NS2. A connection of the port P1 of the Ethernet switchES6 in the network segment NS1 to the port P3 of the Ethernet switch ES8in the network segment NS2 provides the second coupling channel K2 ofthe redundant connection. A programming device PG1, which is attachedvia a port P1 to the port P1 of the Ethernet switch ES1, is used forconfiguring the network on the basis of suitable inputs from a user. Forthis purpose, the programming device PG1 has suitable operatingelements, such as e.g. a display unit and a keyboard, which are notillustrated in the figure for the sake of clarity. The configuration cantake place e.g. with the aid of a web page which is loaded into theprogramming device PG1 from a switch that is to be configured, or withthe aid of a configuration tool, e.g. an SNMP (Simple Network ManagementProtocol) tool which runs on the programming device PG1 as a program. Aspart of the configuration, a logical name which designates the redundantconnection between the two network segments NS1 and NS2 is entered intothe relevant memory M of the Ethernet switches ES5 and ES6. The couplingport which is used for the redundant connection is also stored in therelevant memory M. This is the port P4 in the case of the Ethernetswitch ES5, and the port P1 in the case of the Ethernet switch ES6. In anetwork startup phase, the two Ethernet switches ES5 and ES6 ascertain,by means of distributing special messages in which they enter thelogical name of the redundant connection, the respective other Ethernetswitch ES6 or ES5 belonging to the same redundant connection. Withreference to a defining criterion, e.g. on the basis of the local MACaddress in the network, the two Ethernet switches ES5 and ES6 establishwhich coupling channel is active during error-free operation and whichis deactivated. For the purpose of redundancy monitoring during theredundancy operation, e.g. the Ethernet switch ES6, which has thehighest MAC address in the network, is assigned the function of a masterwhile the Ethernet switch ES5 having the lower MAC address is operatedas a slave. In cyclically transmitted unicast messages, the masternotifies the slave of the status of its coupling port. If the Ethernetswitch ES6 sends “link-up” as the status of the coupling port P1, thecoupling port P4 of the Ethernet switch ES5 remains deactivated.However, if the Ethernet switch ES6 sends “link-down” as the status orif the Ethernet switch ES5 does not receive any more such messages forlonger than a predetermined period, it recognizes the failure of thecoupling channel of the partner device, in this case of the Ethernetswitch ES6, and activates its coupling port P4. Therefore duringerror-free operation, i.e. if the coupling port P1 of the Ethernetswitch ES6 has the status link-up, only the coupling port P1 of theEthernet switch ES6 is active as master. If the coupling port P1 of themaster changes to the status link-down, the coupling port P4 of theEthernet switch ES5 belonging to the same redundant connection isactivated. The cycle time used for sending the messages from the masterdepends on the required reconfiguration time of the network. In the caseof a maximal reconfiguration time of approximately 100 ms, a cycle timeof e.g. 10 ms is preferred, since the network experiences only a limitedadditional load from the cyclically sent messages in this case.

The configuration of the network during the network startup phase isdescribed in greater detail below with reference to the flow diagram inFIG. 2. The method begins at the Start. In a branch T1, the Ethernetswitch checks whether a logical name for the redundant connection, e.g.the name “Network2”, which name is the same for all Ethernet switches ofthe same redundant connection, has already been entered in the relevantmemory M (FIG. 1). As soon as a connection name is entered at theEthernet switch, said switch changes to a status of “no connection”corresponding to an action A1. In this status, the Ethernet switchfunctions as follows:

The Ethernet switch cyclically sends multicast messages comprising a MACmulticast address which is specially defined for the method as adestination address, the unique MAC unicast address of the relevantEthernet switch as a source address, and the logical connection namewhich was assigned to the relevant redundant connection. The couplingport associated with the redundant connection remains deactivated.

As soon as the Ethernet switch which has the status “no connection”receives a valid message containing the above cited defined MACmulticast address, it compares the connection name contained thereinwith that which is stored in the local memory M. If the comparisonproduces a match, the Ethernet switch changes to a status “connectionestablished” corresponding to a path Y following a branch T2 in whichthe comparison took place. Such a receive message can only be themessage of the redundant partner device. The respective other Ethernetswitch associated with the same redundant connection is thereforeidentified.

In an action A2, the Ethernet switch now cyclically sends unicastmessages to the partner device that has been identified. These unicastmessages contain the unique MAC unicast address of the partner device asa destination address, the unique MAC—unicast address of the Ethernetswitch which processes the execution of the method as a source address,and the link status of the defined coupling port. In a branch T3following thereupon, the Ethernet switch checks whether correspondingmessages having the MAC unicast address of the partner device as asource address are received. If this is the case, action A3 takes place.In the context of the action A3, the Ethernet switch establishes thedistribution of master/slave roles. This takes place in accordance witha defining criterion. For example, the Ethernet switch having thehighest MAC unicast address is master. If the Ethernet switch itselfbecomes master, it sends the status of its specified coupling port tothe slave. Depending on the status that is received, the slave activatesor deactivates its coupling port. If the status “link-down” for thecoupling port of the master is received in a message, the coupling portof the slave becomes or remains activated. Conversely, if the status“link-up” is read from the message, the coupling port of the slavebecomes or remains deactivated. This procedure is applied analogouslyduring the redundancy operation which follows “End” in the flow diagram.

As soon as a slave which has the status “connection established” doesnot receive any more messages from the master, it activates the couplingport and changes to the status “no connection”. As a result of this, theredundancy can advantageously be automatically reconfigured followingthe reintroduction of a partner device of a redundant connection.

For diagnostic purposes, the monitoring of the slave can also take placewith the aid of cyclic messages from the slave which are analyzed by themaster.

On the basis of the routine which is shown, it is clear that the methodcan manage the redundant coupling of physical and virtual networksegments, and of network segments in which wireless transmissionsections are combined with wire-based transmission sections.

In the exemplary embodiment shown in FIG. 3, three network segments NS3,NS4 and NS5 are redundantly coupled via two Ethernet switches ES13 andES14. For the purpose of the redundancy configuration, both a logicalname e.g. “Network4” and a logical name e.g. “Network5” are entered inthe respective memories M of the Ethernet switches ES13 and ES14 for theredundant connection between the network segment NS3 and the networksegment NS4 or between the network segment NS3 and the network segmentNS5 respectively. In this case, the coupling port P3 in the Ethernetswitch ES13 and the coupling port P4 in the Ethernet switch ES14 areassigned to the redundant connection “Network4”. The redundantconnection “Network5” is correspondingly assigned the coupling port P4of the Ethernet switch ES13 and the coupling port P1 of the Ethernetswitch ES14. For each redundant connection, the configuration methodruns in the manner described with reference to the FIGS. 1 and 2. If alink-down occurs in relation to a coupling port, e.g. the coupling portP3, and therefore the redundancy is lost for the redundant connection“Network4”, this has no effect on the redundancy of the other redundantconnection “Network5”. The method therefore allows port-selectiveswitching between master and slave, i.e. each redundant connection hasits own redundancy for link-down events.

1. A network having redundancy properties, wherein the network complieswith an Ethernet specification, comprising: at least two networksegments which have a plurality of Ethernet switches, wherein the atleast two network segments are connected to each other via a redundantconnection comprising at least two coupling channels, wherein a firstcoupling channel has a connection of a first port of a first Ethernetswitch which is arranged in the first network segment to a second portof a second Ethernet switch which is arranged in the second networksegment, and wherein a second coupling channel has a connection of athird port of a third Ethernet switch which is arranged in the firstnetwork segment to a fourth port of a fourth Ethernet switch which isarranged in the second network segment; and a programming device tostore a logical name for the redundant connection in the first and thethird Ethernet switch during the configuration of the network, whereinthe first or third port are specified as a coupling port, wherein thefirst and the third Ethernet switches identify, during a network startupphase, the respective other third or first Ethernet switch belonging tothe same redundant connection by distributing special messages in whichthe switches enter the logical name of the redundant connection, andwherein the first and third Ethernet switch determines based upon adefining criterion which coupling channel is active during an error-freeoperation and which is deactivated.
 2. An Ethernet switch for use as afirst Ethernet switch in a network having redundancy properties,comprising: a memory for the first Ethernet switch wherein the firstEthernet switch stores a logical name for a redundant connection of thenetwork in the memory, wherein a first port is specified as a couplingport, wherein the first Ethernet switch sends, in a network startupphase, special messages in which it enters the logical name of theredundant connection and its MAC address, wherein the network has atleast two network segments which have a plurality of Ethernet switches,wherein the at least two network segments are connected to each othervia a redundant connection comprising at least two coupling channels,wherein a first coupling channel has a connection of the first port ofthe first Ethernet switch which is arranged in the first network segmentto a second port of a second Ethernet switch which is arranged in thesecond network segment, and wherein a second coupling channel has aconnection of a third port of a third Ethernet switch which is arrangedin the first network segment to a fourth port of a fourth Ethernetswitch which is arranged in the second network segment, wherein when thefirst Ethernet switch receives a corresponding special message from thethird Ethernet switch the first Ethernet switch identifies the thirdEthernet switch as belonging to the same redundant connection, andwherein the first Ethernet switch determines based upon a definingcriterion which coupling channel is active during an error-freeoperation and which is deactivated.
 3. The Ethernet switch as claimed inclaim 2, wherein the logical names for a second or further redundantconnections are stored in the memory.
 4. The Ethernet switch as claimedin claim 2, wherein the logical names for a second and further redundantconnections are stored in the memory.
 5. The Ethernet switch as claimedin claim 2, wherein the special messages are multicast messages, whereinthe Ethernet switch compares the logical name of a redundant connectioncontained in the special message with its own stored logical name, whenthe special message is received, and wherein in the event of a match theMAC source address contained in the message and the local MAC address isanalyzed as a defining criterion.
 6. The Ethernet switch as claimed inclaim 3, wherein the special messages are multicast messages, whereinthe Ethernet switch compares the logical name of a redundant connectioncontained in the special message with its own stored logical name, whenthe special message is received, and wherein in the event of a match theMAC source address contained in the message and the local MAC address isanalyzed as a defining criterion.
 7. The Ethernet switch as claimed inclaim 4, wherein the special messages are multicast messages, whereinthe Ethernet switch compares the logical name of a redundant connectioncontained in the special message with its own stored logical name, whenthe special message is received, and wherein in the event of a match theMAC source address contained in the message and the local MAC address isanalyzed as a defining criterion.
 8. A method for configuring a networkhaving redundancy properties, comprising: providing a network having atleast two network segments which have a plurality of Ethernet switches,wherein the at least two network segments are connected to each othervia a redundant connection comprising at least two coupling channels,wherein a first coupling channel connects a first port of a firstEthernet switch in the first network segment to a second port of asecond Ethernet switch in the second network segment, and wherein asecond coupling channel connects a third port of a third Ethernet switchin the first network segment to a fourth port of a fourth Ethernetswitch in the second network segment; and storing a logical name for theredundant connection in the first and the third Ethernet switch using aprogramming device during a configuration of the network, wherein thefirst and the third Ethernet switches identify, during a network startupphase, the respective other third or first Ethernet switch belonging tothe same redundant connection by distributing special messages in whichthe switches enter the logical name of the redundant connection, whereinthe first and third Ethernet switch determines based upon a definingcriterion which coupling channel is active during an error-freeoperation and which is deactivated.
 9. The network as claimed in claim1, configured to: designate the first or third Ethernet connected to theactive coupling channel switch as a master; designate the respectiveother third or first Ethernet switch connected to the deactivatedcoupling channel as a slave; cyclically transmit a unicast message fromthe master that notifies the slave of the status of the coupling channelconnected to the master; and if the slave receives a “link down” statusfrom the master, or if the slave does not receive a status from themaster for a predetermined period of time, the slave recognizes afailure of the coupling channel connected to the master, and activatesthe deactivated coupling channel connected to the slave.
 10. TheEthernet switch as claimed in claim 2, configured to: cyclicallytransmit a unicast message that notifies the third Ethernet switch ofthe status of the first coupling channel.
 11. The method as claimed inclaim 8, further comprising: designating the first or third Ethernetswitch connected to the active coupling channel as a master; designatingthe respective other third or first Ethernet switch connected to thedeactivated coupling channel as a slave; the master cyclicallytransmitting a unicast message that notifies the slave of the status ofthe coupling channel connected to the master; and if the slave receivesa “link down” status from the master, or if the slave does not receive astatus from the master for a predetermined period of time, the slaverecognizes a failure of the coupling channel connected to the master,and activates the deactivated coupling channel connected to the slave.